The biorefinery is a key element for an integrated bioresources management. During the Rio de Janeiro congress in June 1992, 170 states have integrated the principle of integrated management into their action programme for the twenty-first century: in September 2002, this principle has even been reasserted during the world summit in Johannesburg. According to the US Department of Energy's definition, the biorefinery is a global plant concept wherein the biomass resource is extracted, then converted to a wide range of upgradable products. The biorefinery logical scheme is borrowed from petrochemistry. The intermediate compounds (sometimes referred to as synthons) derived from sugars occupy a central position since they lead to the final products that will be launched onto the market (Ohara et al., Appl. Microbiol. Biotechnol. 62, 474-477 (2003); Kamm and Kamm, Appl. Microbiol. Biotechnol. 62, 137-145 (2004)). Alcohols and ketones belong to these important synthons obtained from the biomass.
In a biorefinery, the streams of alcohols and of compounds containing a carbonyl group such as mainly acetone can result from the distillation of the fermentation musts or their separation by means of membranes.
Examples of the various fermentation types known to the person skilled in the art and using renewable raw materials of vegetable origin are:                acetonobutylic or ABE (acetone-butanol-ethanol) fermentation mainly using the Clostridium acetobutylicum bacterial species. ABE fermentation produces two main families of compounds, alcohols (ethanol, butanol) on the one hand and a carbonyl-containing compound, acetone, on the other hand (Spivey M. J. (1978): The acetone/butanol/ethanol fermentation. Process Biochem. 13:2-25). In end-of-culture musts, the alcohols are commonly obtained at a concentration ranging between 150 and 190 mM, whereas the final acetone concentration ranges between 85 and 170 mM;        IBE (isopropanol-butanol-ethanol) fermentation that mainly involves the Clostridium bejerinckii strains, formerly classified as Clostridium butylicum. IBE fermentation produces three main alcohols (ethanol, butanol and isopropanol), as well as acetone. The final alcohol concentrations of IBE fermentation are close to those of the ABE fermentation. However, the acetone concentration is generally lower than in the ABE fermentation;        ethanolic fermentation. In a biorefinery, the ethanol is generally obtained from the alcoholic fermentation carried out with the Saccharomyces cerevisiae yeast. It is however possible to use other micro-organisms, notably the Zymomonas mobilis bacterium. With Saccharomyces cerevisiae and the species of Saccharomyces gender, the final ethanol content is close to a hundred grams per liter of medium.        
The substrates of the ABE and IBE fermentations are either simple sugars, monomers or dimers such as glucose and saccharose, respectively, or complex sugars such as starch. The main amylaceous raw materials are cereals (wheat, corn, barley) and potatoes. From amylaceous materials, the monomeric sugars can be obtained by hydrolysis with commercial amylases. However, many Clostridium acetobutylicum and Clostridium bejerinckii strains are capable of using starch directly. With these strains, prior hydrolysis of the starch is thus not necessary. In a similar way to amylaceous substrates, the lignocellulosic substrates can be hydrolyzed by commercial hydrolases (cellulases) in order to give C6 (mainly glucose) and C5 (xylose and arabinose) monomeric sugars. Clostridium acetobutylicum and Clostridium bejerinckii can use C5 as well as C6 monomeric sugars.
Conventionally, the fermentation products are sent to the gasoline pool. In fact, the ABE mixture has a high octane number and, in admixture with gasoline, it causes no stability problems in the presence of water traces or demixing phenomena. Its cetane number is too low to be advantageously incorporated into the diesel fuel pool.
It has been discovered that, by cleverly combining the various streams from the aforementioned fermentation units, according to a chemical acetalization reaction involving at least one alcohol with at least one compound containing a carbonyl group such as ketones, and more precisely acetone, according to the general scheme illustrated below, it is possible to obtain an acetal or a mixture of acetals compatible and soluble with diesel fuels or biofuels and usable in Diesel engines.